Researchers from the University of Wollongong, Australia and the Ulsan National Institute of Science and Technology (UNIST), S. Korea, have developed a germanium oxide/germanium nanocomposite (GeO2/Ge/C) anode material for Li-ion batteries that shows a high capacity of up to 1860 mAh/g at 1 C (2.1 A/g) rate and 1680 mAh/g at 10 C rate. A paper on their work is published in the ACS journal Nano Letters.

They attributed the good electrochemical performance to the increase in reversibility of the conversion reaction of GeO2 by the presence of the elemental germanium nanoparticles present in the composite.

Graphite has been used as the commercial anode material since the introduction of LIBs in the 1990s, although it has a quite low theoretical capacity of 372 mAh/g. Thus, much research has been focused on high capacity materials such as silicon (4200 mAh/g), germanium (1623 mAh/g), and tin (993 mAh/g) to replace the graphite anode. The oxides of these metals (SiO, GeO2, SnO, SnO2) are another group of materials which can provide high lithium storage capacity. In addition, there is widespread belief that, during the first lithiation, Li2O is irreversibly formed. If the Li2O component could be reversibly formed during cycling, these oxide materials could theoretically store up to 8.4 Li+. This would make them attractive alternatives as high capacity anode materials.

Germanium dioxide nanoparticles have been previously studied as anode material for LIBs and were reported to react with up to 9 Li+ during the first discharge cycle. The lithium storage mechanism is described by an initial conversion reaction followed by an alloying reaction. The lithium ions, however, could not be fully removed in the subsequent charging cycle due to the irreversible Li2O formation. This limits the theoretical lithium storage to 4.4 Li+ per GeO2 (1126 mAh/g) compared to 8.4 Li+ (2152 mAh/ g).

Recently, Kim et al. published a report on MGeO3 (M = Cu, Fe, and Co), in which the reversible formation of Ge−O bonds during lithium insertion and extraction was studied using X-ray absorption spectroscopy. One of the key factors contributing to the reoxidation of metallic germanium during delithiation is the presence of the transition metal nanoparticles. The metallic nanoparticles play a catalytic role in the decomposition of Li2O and also form a conductive network between germanium and Li2O to facilitate the reoxidation of germanium...In this work, the catalyst role of Ge in GeO2/Ge/C nanocomposite anode is investigated using partial reduction of the GeO2 in conjunction with the carbon coating process. The anode shows a higher capacity and better rate capability than the GeO2/C nanocomposite.

—Seng et al.

The team synthesized the GeO2/Ge/C anode material using a simple method involving simultaneous carbon coating and reduction by acetylene gas. The nanosized GeO2/Ge particles are coated by a thin layer of carbon, which is also interconnected between neighboring particles to form clusters of up to 30 μm.

Lithium storage performances of GeO2/Ge/C, GeO2/C and GeO2 bulk and nanoparticles were tested in a coin type half-cell.

Based on their testing, the team determined that:

The reversibility of the conversion reaction of GeO2 is related to the carbon coating (GeO2/C) and the introduction of metallic germanium (GeO2/Ge/C).

The nanosize particles are very important to enable the reversible conversion reaction. Nanoparticles have a larger surface area, which promotes the reaction kinetics. In addition, nanoparticles are known to show a smaller absolute volume change, which could keep the Li2O and Ge in close proximity for the decomposition of lithia and simultaneous oxidation of germanium, they suggested.

The carbon coating is an important factor in increasing the reversibility of the conversion reaction. As carbon is highly conductive, the interconnected carbon shells of the GeO2/C and GeO2/Ge/C samples would provide an efficient network for electron transfer, which in turn increases the kinetics of the lithium reactions. The carbon shells also can act as a buffer matrix to limit the volume variation during charge and discharge cycles.

They also confirmed the catalytic effect of germanium in the decomposition of Li2O.

Schematic representation of the lithium reaction mechanism in the different materials. A reversible conversion mechanism of GeO2 can be observed for GeO2-nano, GeO2/C, and GeO2/Ge/C. The nanosized GeO2 particles are crucial for enabling the conversion reaction, while the carbon coating can improve the reversibility. The elemental germanium in GeO2/Ge/C plays a crucial role as a catalyst in improving the reversibility of the conversion reaction of GeO2. Credit: ACS, Seng et al. Click to enlarge.

We found that the nanosized particles, carbon coating, and the elemental germanium in the composite play a crucial role in activating and improving the kinetics of the conversion reaction.

Comments

"(UNIST), S. Korea, have developed a germanium oxide/germanium nanocomposite (GeO2/Ge/C) anode material for Li-ion batteries that shows a high capacity of up to 1860 mAh/g at 1 C (2.1 A/g) rate and 1680 mAh/g at 10 C rate."

Many more 'lower cost' nano-technology materials will be used for higher performance anodes by 2020. This is just the beginning, more will come every month or so.

The proper mix of ultra strong cellulose crystalline (NNC) with plastics and composites will produce highly resistant, ultra light (under 1000 lbs) more aerodynamic (under 0.20) car bodies, in the same time frame.

A small 1000+ Wh/Kg, 100+ kWh battery pack will propel-drive those light weight EVs for 1000+ Km between recharge.

The transition from ICEVs to extended range BEVs will be very fast after 2020 or so.

Note: Toyota's USA/Canada 2012 sales were composed of 14.6% hybrids vs 3.6% for the total USA/Canada sales. Toyota will have 21 new Hybrids on the market by 2015 and expected sales will reach 25+%. Others will start to catch up between 2015 and 2020?

Half cells allow you to know the capacity, but not the decay rate. Let me see, contact politician, say you have a new anode material. Choose any junk you want. Test in half cells and never do full cell testing. Continue to say it looks promising but needs more work. Make a career out of it. Don't succeed, because the money stops and you will be out of a job. Your politician is only interested in having an excuse to send pork to his district. Works like that in roo land too.